Something Loopy in Assigning Strings

I tried this in desperation after strcat() refused to work. I just want to concatenate three strings. Can anyone tell me why this doesn't work? I can see the creation of "10", but not of "11", though there's plenty of room on the disk for both. Moreover, if I ask for a printf of fieldn and strlen(fieldn) for all three fields, I get the right responses. field1[] is more than long enough to handle the job.

That's just silly. Disk operations are orders of magnitude slower than memory operations. Use strcat or strncat. They work. If you can't get them to work, show THAT code not this grossly over-footprint, underperforming stuff.